Prince George’s County has approved plans for a high-end residential and retail development adjacent to the University of Maryland that many hope will spur economic activity on the relatively barren east side of campus. Called Domain College Park, the massive development planned for the intersection of Mowatt Lane and Campus Drive would include 256 luxury apartments, 10,000 square feet of retail and a 380-space parking garage. Houston-based developer Hanover Cos. officials told the Prince George’s County Planning Board Thursday they hope to capitalize on the planned development of Metro’s Purple Line through the area. “The goal of this project is, it’s a linchpin for the area — it’s a gateway to the university,” said Adam Harbin, a partner at Hanover. “As that happens, this entire submarket will redevelop.”